Anyone experience popping sound when switching channel?

[Tom Phillips]

Re: the Physics forum guy who said "I have to bail out for the day"
I wonder if that also meant "It's the end of the work day so I gotta stop surfing the internet on my employer's time and go home."

[loudthud]

Maybe his only computer access is in the prison library.

What does Peavey use for muting on the 5150? Was it a triac?

[Enzo]

Peavey 5150 and similar use a JFET for muting the signal path, but there is a small triac driving the JFET gate. I believe they do that because the triac will trigger on rising or falling signals, useful when it is watching a relay coil current on or off.

[J M Fahey]

Clever chaps these Peavey guys

And yes, contrary to most other active devices, triacs can be triggered with signals from both polarities , which is put to good use here.

The idea is that any signal, (voltage change) any polarity which can pop , is detected by them and triggers muting for a few milliseconds.

Clap clap hats off to Peavey

[Alan0354]

Sorry I have not come back on this thread. I want to spend the time studying SCR, Triac and phototriac before I come back and talk. This is one subject I never used in my life and I had to spend last night and studying. I am looking at this part:http://www.vishay.com/docs/83627/il410.pdf.


I want to confirm from reading the application notes and the data sheet.

1) Both the zero crossing and non zero crossing act like a short circuit ( almost) as long as I supply the current to the LED higher than the minimum trigger current. So if I apply the current to the LED, I short out the signal.

2) I should not use zero crossing phototriac because there is a delay after the start of the trigger signal until the zero crossing. I should use the non zero crossing as the device turns on as soon as you apply the current to the LED. I afraid a little bit of the signal might go through because of the delay.

3) There are still some voltage develop across the triac, so there is a clipped signal going into the power amp even the triac is on.

I think all in all, the Vactrol should be a better choice as it is just a resistor that becomes low resistance when the LED is on, and high resistance when LED is off. So far VTL5C3 or Silonex NSL 32SR3 look promising. The turn off time is about 0.1 sec to 1M.

Again, Vactrol is completely new to me. This is one subject I just never encountered in my life.

[Alan0354]

Google is your friend [tm] , 65400 results in:
https://www.google.com/search?q=zero...x-a&gws_rd=ssl

That said, yes, in that point I was being sarcastic, not about you , my friend, but about Physics Forum user berkeman, who first used complex sounding names (to impress???) in his answer but when you asked him for clarification he retorted:

No kidding !!!
And then to avoid further questions from you he added:


It wasn´t me only, Physics Forum user davenn made fun of him too ... with good reason.
Besides his "bailing out" when asked for details, the *main* problem is that LDR are WAY too slow for zero crossing synchronized anything so his answer was 100% BS from the beginning.
As a side note, I never ever make fun at beginners/noobs/etc. , quite the opposite, will go to great efforts to simplify and explain things, but when somebody comes in a pompous way yet showing absolute lack of skills in the area he claims, well, he´s fair game
In a light, finger ribbing way, of course
For me, MEF is akin to a late Friday night meeting of old friends, relaxing around a few beers.
Meaning it´s a FUN place

I don't frequent there much anymore, so I am not going to defend them either. Berkeman usually know his stuff, just this might be something he doesn't know. This applies to me as I never in my life use a SCR or Vactrol. When I looked at the symbol in the Soldano schematic, I know it's a opto resistor, but I cannot find the part by typing it on web. It was not until Nashvillebill gave me the link, I don't know the name is Vactrol.

[Pedro Vecino]

Capacitor between the coil of the relay usually has no noticeable effect if you have a reverse diode. But that same capacitor (1uF) between the switch pins (6V) usually have it. I use it always

Thanks. What do you mean by the switch pins?

A 1uF cap connected to the terminals of the switch through wich the relay is activated. If you use an output jack to connect an external footswitch to activate the relay, then between the terminals of the output jack itself.
When I use relay switching to activate/deactivate a complete loop circuit (inserting it between master and driver input) I send to the switch the negative line previously connected to ground for reference. The positive line, direct to the relay connector.
If it works good assigning a loop (in and out), it should work by selecting two preamp outputs to the driver input without problems, I imagine.

[Alan0354]

THis is the circuit I designed, see whether anyone has comment.



As you can see, the channel switching switch at the lower left can generate both rising and falling edge depending on either from clean to OD or wise verse. So I use two monostable FF one capture the rising edge and the other capture the falling edge. the Vactrol is turned on by the low going pulse of about 10mS from the /Q of the FF. 1N4148 is used to isolate one side from the other. So whenever the switch change state, a mute of about 10mS + 50mS of the delay is generate. So the mute is about 60mS to 100mS.

The vectrol short out the signal from the preamp to the PI for about 60 to 100mS.

The 74HC221 non retriggerable monostable FF is used to debounce the channel switch. S1C, S2C and S3C are the coils of the channel switching relays. I am counting on the flyback of the relay coil to give me a fast rising edge.

[Alan0354]

Hi, if nobody sees any problem by the end of today, I'll start ordering parts. I already ordered the vactrol Silonex NSL-32SR3 as they sell it on ebay 4 for about $10+shipping.

One other question. I saw Peavey 5150 uses a p-JFET for shorting the signal for muting. I have issue with that because in order for the FET to stay off in normal operation, the gate has to be pulled up to +22V to ensure the FET remain "off" when the signal swing to +20V. The problem is the J174 spec that the max gate to source reverse voltage is 30V only. This means if the signal swing to over -8V, it would exceed -30V and damage or burn the FET. I did not see any JFET that can withstand over 40V in Digikey. If you can find a JFET that can take 60V or higher, that will work.

that's the main reason I decided not to go with the FET route.

[loudthud]

Remember the specs you see on a data sheet are minimums in the case of breakdown voltage. I just put a J175 on the curve tracer and V(gss) measured 43V. Three J176 all measured 50V.

[Alan0354]

Remember the specs you see on a data sheet are minimums in the case of breakdown voltage. I just put a J175 on the curve tracer and V(gss) measured 43V. Three J176 all measured 50V.

According to Fairchild, it is also the Absolute Max rating.http://pdf.datasheetcatalog.com/data...child/J176.pdf
I can only read from the spec. From my experience, SS device really mean when they give the Absolute Maximum and Minimum. Yes, You can hand pick individual device, but it is not adviceable in production. They are really not like tubes and transformers.....that people push it. SS device really burn if you push beyond.

But in this case, because the driving circuit are high impedance, I don't think burning is an issue, more like clipping the signal when it conducts. Ha ha, maybe that gives the character of the sound!!!! When you clip, you introduce a DC offset and change the waveform a little.

[Gingertube]

Alan,
"Capturing" the switching edges and using them to "fire" a shunt signal to 0V mute circuit is a good idea to eliminate any switching pop.
BUT - it can be done more simply.
I was initially going to say check out the Mesa Subway Rocket schematics here:
http://www.classictubeamps.com/schem...0schematic.pdf
LDR2 does the muting. I think this circuit is also too complicated.

Just differentiate the relay switching signal (AC couple) to pick up the edges, use a diode clamp to select the leading edge only and set the time constant for about 10ms. 1 cap, 1 R and one transistor should be all that is needed to drive the shunt element.JFETs as the shunt element are nice but often can't be used due to voltage withstand problems, I often use the old H11F Optocoupler for this sort of duty.
http://www.datasheetarchive.com/dlma...f-00074122.pdf

Cheers,
Ian

[loudthud]

According to Fairchild, it is also the Absolute Max rating.

Where is says Absolute Maximum Ratings*, those are just the drive by specs. The actual test limits are under Electrical Characteristics. Under Test Conditions for B(br)gss is says 1uA Vds=0V (Source and Drain are shorted) minimum value = 30V. Translation: They apply 30V to the Gate and if the current is less than 1uA, the device passes. These days they don't test every paramater on every device after packaging. They qualify the wafer after processing by probing devices in each corner, package the parts and then maybe do a continunity check to make sure the bond wires didn't break. A small sample of the lot might be fully tested. If the number of bad devices exceeds some number, the whole lot is rejected.

[Alan0354]

Alan,
"Capturing" the switching edges and using them to "fire" a shunt signal to 0V mute circuit is a good idea to eliminate any switching pop.
BUT - it can be done more simply.
I was initially going to say check out the Mesa Subway Rocket schematics here:
http://www.classictubeamps.com/schem...0schematic.pdf
LDR2 does the muting. I think this circuit is also too complicated.

Just differentiate the relay switching signal (AC couple) to pick up the edges, use a diode clamp to select the leading edge only and set the time constant for about 10ms. 1 cap, 1 R and one transistor should be all that is needed to drive the shunt element.JFETs as the shunt element are nice but often can't be used due to voltage withstand problems, I often use the old H11F Optocoupler for this sort of duty.
H11F1 ... - Datasheet Search Engine Download

Cheers,
Ian

Yes, the optoFET looks good. You think +/-30V limit is good enough? I looked in Digikey, the best is +/-30V or 60Vpp. I wonder there are higher voltage ones. The Vactrol is 60V which I assume is in either direction as it's only a resistor. The concern of Vectrol is the turn off time is very slow.

What do you mean by diode clamp to select the leading edge?

[Alan0354]

Where is says Absolute Maximum Ratings*, those are just the drive by specs. The actual test limits are under Electrical Characteristics. Under Test Conditions for B(br)gss is says 1uA Vds=0V (Source and Drain are shorted) minimum value = 30V. Translation: They apply 30V to the Gate and if the current is less than 1uA, the device passes. These days they don't test every paramater on every device after packaging. They qualify the wafer after processing by probing devices in each corner, package the parts and then maybe do a continunity check to make sure the bond wires didn't break. A small sample of the lot might be fully tested. If the number of bad devices exceeds some number, the whole lot is rejected.

It is right on the first page. It also specified with a "*" that "These rating are limiting values that above which the serviceability of any semiconductor device may be impaired.

Unlike the tubes or transformers, these semiconductor devices are microscopic in size and with parasitic components during the process of forming the die. Some can latch up similar to SCR being turn on due to over voltage. The stand off voltage are guaranty by design. If it is designed for certain voltage, you should really follow it.